Added code to import a developer profile.

This is the same procedure people do when they get a new Mac for
development. This enables the key signing.
Unlock the keychain

Although when a key chain is first created it appears unlocked.
this can be null
added help
Look into the developer profile and show what's in it.
a bit of test driver code to understand how to interact with PKCS12 and PKCS7 files
added the logic of destroying and recreating a key
Merge pull request #34 from kohsuke/master

Added an ability to import *.developerprofile into a build